US3764751A

US3764751A - Method and apparatus for synchronizing the operation of trunk scanners

Info

Publication number: US3764751A
Application number: US00285976A
Authority: US
Inventors: R Padgett
Original assignee: GTE Automatic Electric Laboratories Inc
Current assignee: AG Communication Systems Corp
Priority date: 1972-09-05
Filing date: 1972-09-05
Publication date: 1973-10-09
Anticipated expiration: 1990-10-09
Also published as: CA979554A

Abstract

In a system having a pair of trunk scanners which are operated in synchronism to provide redundancy in case of failures, with one trunk scanner being ''''on line'''' and the other being ''''on standby,'''' means are disclosed by bringing a trunk scanner into synchronism with the trunk scanner which is ''''on line,'''' when the other is returned to ''''standby'''' operation. Generally, this is accomplished by the contents of a last address word read from memory and used to trigger an address generator to advance to a start address or first programmed word. This last address word is simultaneously coupled to and used to trigger the address generator associated with the other trunk scanner to likewise cause it to advance to the start address word, thus causing the address generators associated with each of the trunk scanners to simultaneously advance and to place the trunk scanners into synchronism.

Description

United States Patent [191 Padgett SYSTEM METHOD AND APPARATUS FOR SYNCHRONIZING THE OPERATION OF TRUNK SCANNERS Richard A. Padgett, Lombard, Ill.

GTE Automatic Laboratories Incorporated, Northlake, lll.

Sept. 5, 1972 US. Cl. 179/18 FG Int. Cl.

Field of Search l79/l8 PG, 18 ES References Cited UNITED STATES PATENTS NETWWK MARKER I6 I l [451 Oct. 9, 1973 Primary Examiner-William C. Cooper Att0rneyK. Mullerheim et al.

[57] ABSTRACT In a system having a pair of trunk scanners which are operated in synchronism to provide redundancy in case of failures, with one trunk scanner being on line" and the other being on standby, means are disclosed by bringing a trunk scanner into synchronism with the trunk scanner which is on line, when the other is returned to standby operation. Generally, this is accomplished by the contents of a last address word read from memory and used to trigger an address generator to advance to a start address or first programmed word. This last address word is simulta neously coupled to and used to trigger the address 5 Claims, 6 Drawing Figures 2O IEXISHNG QDLOCATED 8/17 7 W mNNECT l l OPERATOR l I l 16 l SENDER I m REMOTE 19 OPERATOR l POS/T/ON I SENDER P l L .L l

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I 3 E .56 Em En 02 t Ewmm m m 7 3m Em ta. Q2 N n 3m Cw v. m 52. So am mach mm 5: mm. A 858$? T. k k v Em mmEm mm oz 8 BBQ 02 Em wfi oz Pi IE1: mm: o2 mm; 2E 02 v 02 m: n u T m mum mm: u 3 WE .Ew 5n Y 02 Q2 kw fi fi A H Yll 826% u wmnmuw mm; .Em Q2 .8 mm: :5 n Ei E Q METHOD AND APPARATUS FOR SYNCHRONIZING THE OPERATION OF TRUNK SCANNERS FIELD OF THE INVENTION This invention relates to a centralized automatic message accounting system. More particularly, it relates to an improved method and apparatus for synchronizing the operation of the trunk scanners provided in such a system.

In systems such as the hereinafter disclosed centralized automatic message accounting system, the electronic common control area thereof generally is duplicated to provide redundancy in case of failures. These duplicated systems normally are operated synchro nously, with each redundant system being capable of handling the entire traffic load. The synchronous operation of the duplicated systems also allows for comparison of some signal leads, for detecting failures by comparing operations of the duplicated systems.

In the disclosed centralized automatic message accounting system the trunk scanner is part of the electronic common control area, and duplicate trunk scanners are provided and operated in synchronism. If both trunk scanners are fully operational, the trunk scanners run synchronously and perform identical functions at the same time. Only one, however, is on line," and the other is on standby."

lf one of the trunk scanners fails, it is placed on repair. After the fault is corrected, it is returned to standby" so that it can be placed on line in the event the other trunk scanner should fail.

lt is obvious that the trunk scanner which is placed on repair and subsequently returned to standby service will no longer be in synchronism with the on line trunk scanner. Accordingly, some method or means must be provided to bring both trunk scanners into synchronism.

Accordingly, it is an object of the present invention to provide an improved centralized automatic message accounting system.

More particularly, it is an object to provide in such a centralized automatic message accounting system an electronic control area which is duplicated to provide redundancy in case of failures, the duplicated systems being operated synchronously.

More particularly still, it is an object to provide an improved method and means for synchronizing the duplicated systems, particularly the trunk scanners thereof.

The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others and the apparatus embodying features of constructon, combination of elements and arrangement of parts which are adapted to effect such steps, all as exemplified in the following detailed disclosure, and the scope of the invention will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings in which:

FIG. 1 is a functional block diagram of the centralized automatic message accounting system;

FIG. 2 illustrates the trunk scanner memory layout;

FIGS. 3-5 are a flow chart of the trunk scanner operations; and

FIG. 6 is a block diagram schematic of a portion of the trunk scanners and the maintenance subsystem, illustrating the manner in which the trunk scanners are brought into synchronism.

DESCRIPTION OF THE INVENTION Referring now to the drawings, in FIG. 1 the centralized automatic message accounting system is illustrated in block diagram, and the functions of the principal equipment elements can be generally described as follows. The trunks 10, which may be either multifrequency (MF) trunks or dial pulse (DP) trunks, provide an interface between the originating office, the toll switching system, the marker 1 l, the switching network 12, and the billing unit 14. The switching network 12 consists of three stages of matrix switching equipment between its inlets and outlets. A suitable distribution of links between matrices are provided to insure that every inlet has full access to every outlet for any given size of the switching network. The three stages, which consist of A, B and C crosspoint matrices, are interconnected by AB and BC links. The network provides a minimum of inlets, up to a maximum of 2,000 inlets and 80 outlets. Each inlet extends into an A matrix and is defined by an inlet address. Each outlet extends from a C matrix to a terminal and is defined by an outlet address.

Each full size network is divided into a maximum of 25 trunk grids on the inlet side of the network and a service grid with a maximum of 16 arrays on the outlet side of the network. The trunk grids and service grid within the networks are interconnected by the BC link sets of 16 links per set. Each MF trunk grid is provided for 80 inlets. Each DP turnk grid is provided for 40 inlets. The service grid is provided for a maximum of 80 outlets. A BC link is defined as the interconnection of an outlet of a B matrix in a trunk grid and an outlet of a C matrix in the service grid.

The marker 11 is the electronic control for establishing paths through the electromechanical network. The marker constantly scans the trunks for a call for service. When the marker 11 identifiesa trunk with a call for service, it determines the trunk type, and establishes a physical connection between the trunk and a proper receiver 16 in the service circuits 15.

The trunk identity and type, along with the receiver identity, are temporarily stored in a marker buffer 17 in the call processor 18 which interfaces the marker 11 and the call processor 18.

When the call processor 18 has stored all of the information transmitted from a receiver, it signals the marker 11 that a particular trunk requires a sender 19. The marker identifies an available sender, establishes a physical connection from the trunk to the sender, and informs the call processor 18 of the trunk and sender identities.

The functions of the receivers 16 are to receive MF 2/6 tones or DP signals representing the called number, and to convert them to an electronic 2/5 output and present them to the call processor 18. A calling number is received by MP 2/6 tones only. The receivers will also accept commands from the call processor 18, and interface with the ONI trunks 20.

The function of the MF senders are to accept commands from the call processor 18, convert them to MF 2/6 tones and send them to the toll switch.

The call processor 18 provides call processing control and, in addition, provides temporary storage of the called and calling telephone numbers, the identity of the trunk which is being used to handle the call, and other necessary information. This information forms part of the initial entry for billing purposes in a multientry system. Once this information is passed to the billing unit 14, where a complete initial entry is formated, the call will be forwarded to the toll switch for routing.

The call processor 18 consists of the marker buffer 17 and a call processor controller 21. There are 77 call stores in the cail processor 18, each call store handling one call at a time. The call processor 18 operates on the 77 call stores on a time-shared basis. Each call store has a unique time slot, and the access time for all 77 call stores is equal to 39.4 MS, plus or minus 1 percent.

The marker buffer 17 is the electronic interface between the marker 11 and the call processor controller 21. lts primary functions are to receive from the marker 11 the identities of the trunk, receiver or sender, and the trunk type. This information is forwarded to the appropriate call store.

The operation of the call process controller revolves around the call store. The call store in a section of memory allocated for the processing of a call, and the call process controller 21 operates on the 77 call stores sequentially. Each call store has 8 rows and each row consists of 50 bits of information. The first and second rows are repeated in

rows

7 and 8, respectively. Each row consists of 2 physical memory words of 26 bits per word. 25 bits of each word are used for storage of data, and the 26th bit is a parity bit.

The call processor controller 21 makes use of the information stored in the call store to control the progress of the call. It performs digit accumulation and the sequencing of digits to be sent. It performs fourth digit /1 blocking on a 6 or 10 digit call. It interfaces with the receivers 16, the senders 19, the code processor 22, thebilling unit 14, and the marker buffer 17 to control the call.

The main purpose of the code processor 22 is to analyze call destination codes in order to perform screening', prefixing and code conversion operations of a nature which are originating point dependent. This code processing is peculiar to the needs of direct distance dialing (DDD) originating traffic and is not concerned with trunk selection and alternate routing, which are regular translation functions of the associated toll switching machine. The code processor 22 is accessed only by the call processor 18 on a demand basis.

The billing unit 14 receives and organizes the call billing data, and transcribes into onto magnetic tape. A multi-entry tape format is used, and data is entered into tape via a tape transport operating in a continuous recording mode. After the calling and called director numbers, trunk identity, and class of service information is checked and placed in storage, the billing unit 14 is accessed by the call process controller 21. At this time, the call record information is transmitted into the billing unit 14 where it is formated and subsequently recorded on magnetic tape. The initial entry will include the time. Additional entries to the billing unit 14 contain answer and disconnect information.

The trunk scanner 25 is the means of conveying the various states of the trunks to the billing unit 14. The trunk scanner 25 is connected to the trunks by a highway extending from the billing unit 14 to each trunk. Potentials on the highway leads will indicate states in the trunks.

Each distinct entry (initial, answer, disconnect) will contain a unique entry identity code as an aid to the electronic data processing (EDP) equipment in consolidating the multientry call records into toll billing statements. The billing unit 14 will provide the correct entry identifier code. The magnetic tape unit 26 is comprised of the magnetic tape transport and the drive, storage and control electronics required to read and write data from and to the 9 channel billing tape. The read function will allow the tape unit to be used to update the memory.

The recorder operates in the continuous mode at a speed of 5 inches per second, and a packing density of 800 bits per inch. Billing data is recorded in a multientry format using a 9 bit EBCDIC character (extended binary coded decimal interchange code). The memory subsystem 30 serves as the temporary storage of the call record, as the permanent storage of the code tables for the code processor 18, and as the alterable storage of the trunk status used by the trunk scanner 25.

The core memory 31 is composed of ferrite cores as the storage elements, and electronic circuits are used to energize and determine the status of the cores. The core memory 31 is of the random access, destructive readout type, 26 bits per word with 16 K words.

For storage, data is presented to the core memory data registers by the data selector 32. The address generator 33 provides the address or core storage locations which activate the proper read/write circuits representing one word. The proper clear/write command allows the data selected by the data selector 32 to be transferred to the core storage registers for storage into the addressed core location.

For readout, the address generator 33 provides the address or core storage location of the word which is to be read out of memory. The proper read/restore command allows the data contained in the word being read out, to be presented to the read buffer 34. With a read/restore command, the data being read out is also returned to core memory for storage at its previous location.

The method of operation of a typical call in the system, assuming the incoming call is via an MP trunk can be described as follows. When a trunk circuit 10 recognizes the seizure from the originating office, it will provide an off-hook to the originating office and initiate a call-for-service to the marker 11. The marker 11 will check the equipment group and position scanners to identify the trunk that is requesting service. Identification will result in an assignment of a unique 4 digit 2/5 coded equipment identity number. Through a trunktype determination, the marker 1 1 determines the type of receiver 16 required and a receiver/sender scanner hunts for an idle receiver 16. Having uniquely identi tied the trunk and receiver, the marker 11 makes the connection through the three-stage matrix switching network 12 and requests the marker buffer 17 for service.

The call-for-service by the marker 11 is recognized by the marker buffer 17 and the equipment and receiver identities are loaded into a receiver register of the marker buffer 17. The marker buffer 17 now scans the memory for an idle call store to be allocated for processing the call, under control of the call process for a duration of no less than 50 milliseconds of digit and 50 millseconds of interdigital pause for storage in the called store. After receipt of ST, the call processor controller 21 will command the receiver 16 to instruct the trunk circuit to return an off-hook to the calling office, and it will request the code processor 18.

The code processor 18 utilizes the called number to *check for EAS blocking and other functions. Upon completion of the analysis, the code processor 18 will send to the call processor controller 21 information to route the call to an announcement or tone trunk, at up to 4 prefix digits if required, or provide delete information pertinent to the called number. If the call processor controller 21 determined that the call is an ANI call, it will receive, accumulate and store the calling number in the same manner as was done with the called number. After the call process controller 21 receives ST." it will request the billing unit 14 for storage of an initial entry in the billing unit memory. It will also command the receiver 16 to drop the trunk to receiver connection. The call processor controller 21 now initiates a request to the marker 11 via the marker buffer 17 for a trunk to sender connection. Once the marker 11 has made the connection and has transferred the identities to the marker buffer 17, the marker buffer will dump this information into the appropriate call store. The call processor controller 21 now interrogates the sender 19 for information that delayed dial has been removed by the routing switch (crosspoint tandem or similar). Upon receipt of this information the call processor controller 21 will initiate the sending of digits including KP and ST. The call process controller 21 will control the duration of tones and interdigital pause. After sending of ST, the call processor 18 will await the receipt of the matrix release signal from the sender l9. Receipt of this signal will indicate that the call has been dropped. At this time, the sender and call store are returned to idle, ready to process a new call.

The initial entry information when dumped from the call store is organized into the proper format and stored in the billing unit memory. Eventually, the call answer and disconnect entries will also be stored in the billing unit memory. The initial entry will consist of approximately 40 characters and trunk scanner 25 entries for answer or disconnect contain approximately characters. These entries will be temporarily stored in the billing unit memory until a sufficient number have been accumulated to comprise one data block of 1,370 characters. Once the billing unit memory is filled, the magnetic tape unit 26 is called and the contents of the billing unit memory is recorded onto the magnetic tape.

The final result of actions taken by the system on a valid call will be a permanent record of billing information stored on magnetic tape in multi-entry format consisting of initial, answer, and disconnect or forced disconnect entries.

Answer timing, force disconnect timing and other timing functions such as, for example, a grace period" timing interval on answer, in the present system, are provided by the trunk timers. These trunk timers are memory timers, and an individual timer is provided for each trunk in a trunk scanner memory which, as can be best seen in FIG. 2, which illustrates the memory layout, comprises a status section and a test section.

The status section contains 1 word per ticketed trunk. Each word contains status, instruction, timing and sequence information. The status section also provides 1 word per trunk group which contains the equipment group number, and an equipment position tens word that identifies the frame. A fully equipped status section requires 2761 words of memory representing 2000 trunks spread over 60 groups plus a status section start word. As each status word is read from memory, it is stored in a trunk scanner read buffer (not shown). The instruction is read by a scanner control to identify the contents of the word. The scanner control logic acts upon the timing, sequence and status information, and returns the updated word to the trunk scanner memory and it is written into it for use during the next scanner cycle.

The test section contains a maximum of 83 words: a start word, a last programmed word, 18 delay words, 2 driver test words, 1 end-test word and l word for each equipment group. The start test word causes a scan point test to begin. The delay words allow time for scan point filters to charge before the trunk groups are scanned, with the delay words containing only instructional data. The equipment group words contain a 2 digit equipment group identity and 5 trunk frame equipped bits. The trunk frame equipped bits (I per frame) indicates whether or not a frame exists in the position identified by its assigned bit. The delay words following the equipment group allow the scan point filters to recharge before the status section of memory is accessed again for normal scanning. The Last Program word inhibits read and write in the trunk scanner memory until a trunk scanner address generator has advanced through enough addresses to equal the scanner cycle time. When the cycle time expires, the trunk scanner address generator returns to the start of the status section of memory and normal scanning recommences.

The trunk scanner memory and the trunk scanner read buffer are not part of the trunk scanner 25, however, the operation thereof is controlled by a scanner control which forms a part of the trunk scanner 25 of the billing unit 14. The trunk scanner 25 maintains an updated record of the status of each ticketed trunk, determines from this status when a billing entry is required, and specifies the type of entry to be recorded. The entry includes the time it was initiated and the identification of its associated trunk.

Scanning is performed sequentially, by organizing the memory in such a manner that when each word is addressed, the trunk assigned to that address is scanned. This causes scanning to progress in step with the trunk scanner address generator. During the address advance interval, the next scanner word is addressed and, during the read interval, the word is read from memory and stored in the trunk scanner read buffer. At this point, the trunk scanner 25 determines the operations to be performed by analyzing the word instruction.

Referring now to FIGS. 3, 4 and 5, which are flow charts of the trunk scanner operations, the operation of the latter as well as the trunk timer can be described.

As indicated above, scanning is performed sequentially. If all trunks in all groups are scanned in numerical sequence beginning with trunk 0000, scanning would proceed in the following manner:

Step 1. Trunk 0000 located in frame (lineup 0, column 0) in the top file, leftmost card position would be scanned first.

Step 2. All trunks located in frame 00 and the leftmost card position would be scanned next from the top file to the bottom.

Step 3. Scanning advances to frame 01 lineup 0, column l) and-proceeds as in Step 2.

Step 4. Scanning proceeds as in Step 3 until frame 04 has been scanned.

Step 5. The scanner returns to frame 00 and Step 2 is repeated for the next to leftmost card position.

Step 6. The sequence just described continues until all ten card positions in all 5 columns have been examined. Step 7. The entire process is repeated in lineups 1 through 5.

When a memory word instruction identifies a trunk group word, the status receivers are cleared to prepare for scanning the trunks specified in the group word. The trunk group digits stored in the trunk scanner read buffer (TSRB) are transferred into the equipment group register.

After the trunk group number is decoded, it is transformed into binary code decimals (BCD), processed through a l-out-of-N check circuit, and applied to the AC bus drivers (ACBD). The drivers activate the scan point circuits via the group leads and the trunk status is returned to the receivers.

A group address applied to the drivers causes the status of all trunks in l lineup and 1 card position and all columns to be returned to the receivers. The group tens digit specifies the trunk frame lineup and the group units digit identifies the card slot.

When a status word is read from memory, it sets the previous count of a trunk timer (TT) into the trunk timer.

if the trunk is equipped and the forced disconnect sequence equals 2 (FDS=2), a request to force: release the trunk is transmitted to the marker 11. If F DS does not equal 2, the present condition of the ticketing contacts in the trunk is tested. If the instruction indicates that the trunk is in an updated condition (the trunks associated memory word was reprogrammed) it is tested for idle. If the trunk is idle, its instruction is changed to denote that it is ready for new calls. If the trunk is not idle, no action is taken and the trunk scanner 25 proceeds to the next trunk.

lf the trunk is not in the updated condition and FDS=3, the trunk is tested for idle. If the trunk is idle, FDS is set to 0 and TT is reset.

If FDS does not equal 3 and a match exists between the present contact status and the previous contact status stored in memory (bits 5 and 6) the FDS memory bits are inspected for a count equal to 1. If FDS=1, TT is reset and the memory contact status is updated. If FDS does not equal 1, TT is not reset.

During any analysis of a trunk status, a change in the contact configuration of a trunk is not considered valid until it has been examined twice.

One bit (SFT) is provided in each memory status word to indicate whether or not a change in status of the trunk was detected during the previous scan cycle.

When a change in status is detected, SFT is set to 1. If SFT=1 on the next cycle, the status is analyzed and SFI is set to 0.

If a mismatch exists between the present contact condition and that previously stored in memory, the status has changed and a detailed examination of the status is started.

If CT=1 the trunk is busy and so the previous condition of the contact is inspected. If the trunk previously was idle, CM=O. Before continuing the analysis, it must be determined if this is the first indication of change in the trunk status by examining the second look" bit (SFT). If SFT=O, it is set to equal 1, and the analysis of this trunk status is discontinued until the next scanner cycle. If SFT=1, the memory status is updated and SFT is set to equal 0.

If CT=l, the trunk is cut through and CM is inspected to determine if the memory status was updated. If CM=l, the GT contact status must differ from GM since it was already determined that a mismatch exists. If GT=0, answer has not occurred. if GT=l, and this condition existed during the previous scan cycle, SFT=-l also. If these conditions are true the FDS does not equal l, TT is advanced and answer timing begins. If these conditions persist for 8 scanner cycles (approximately 1 second), answer is confirmed and an entry will be stored in the trunk scanner formater (TSF). lf answer is aborted (possibly hookswitch fumble) before the 1 second answer time (time is adjustable) expires, TT remains at its last count. When the answer condition returns, answer timing continues from the last TT count. Thus, answer timing is cumulative.

Afer an answer entry is stored, which includes the TT count, TT is reset, SFT is set to 0, and the new contact status is written into memory.

If a mismatch exists and CT=O, the previous state of this contact is inspected by examining bit 5 in the trunk scanner read buffer (TSRB). If CM=l the state of the terminating end of the trunk is tested. lf GT=l, then the condition of the trunk has just changed from answer to disconnect. If this condition existed during the previous scan cycle, SFT=1 and a disconnect entry is stored in the TSF.

After the disconnect entry is stored, which includes the TT count, TT is reset, FDS and SFT are set to 0, and the new status is written into memory.

If a mismatch exists and the originating end of a trunk is not released, both CT and CM equals 1. If GT=0 after the previous scan cycle, FDS is tested. If this change just occurred, FDS does not equal 1. Since FDS does not equal 1, it will be set equal to l and TT will reset. FDS=1 indicates that forced disconnect timing is in progress.

While the conditions just described exist, i.e., mismatch, CT=l, CM=l, GT=O and FDS=1, TT will advance 1 count during each scanner cycle, if k second has elapsed since the last scan cycle. TT will continue to advance until it reaches a count of 20 (approximately 10 seconds) when a forced disconnect entry will be stored in the TSF.

When the entry is stored, FDS is set at 2 indicating that the trunk is to be force released. After the entry is stored, which includes the TT count, TT is reset, SFT is set to 0, and the new status is written into memory.

After the status and test sections of the memory have been accessed, the Last Program word is read from memory and stored in the trunk scanner read buffer.

This word causes read/write in the trunk scanner portion of memory to be inhibited and deactivates the scan point test. The trunk scanner address generator will continue to advance, however, until sufficient words have been addressed to account for one scan cycle. When a predetermined address, the Last Address, is reached, block read/write is removed and the address generator returns to the Start Address (First Program Word) of the scanner memory.

As indicated above, the electronic control area in systems such as the described centralized automatic message accounting system usually is duplicated to provide redundancy in case of failures. For this reason, duplicate trunk scanners 25 are provided, and operated in synchronism. If both of these trunk scanners are fully operational, they run synchronously and perform identical functions at the same time. Only one of the trunk scanners, however, is on line," while the other is on standby.

If one of the trunk scanners fails, it is placed on repair." After the fault is corrected, it is returned to standby" so that it can be placed on line in the event the other trunk scanner should fail.

When the trunk scanner is placed on standby after being returned to service, it must be brought into synchronism with the one already on line. The manner in which this is accomplished is as follows.

As described above, scanning is performed sequentially, by organizing the memory in such a manner that when each word is addressed, the trunk assigned to that address is scanned. This causes scanning to progress in step with the trunk scanner address generator.

During the address interval, the next scanner word is addressed. In the read interval, the word is read from memory and stored in a trunk scanner read buffer. At this point, the trunk scanner determines the operations to be performed by analyzing the word instruction.

After the status and test sectons of the memory have been accessed, the Last Program Word is read from memory and stored in the trunk scanner read buffer. This word causes read/write in the trunk scanner portion of the memory to be inhibited and deactivates the scan point test. The trunk scanner address generator continues to advance, until sufficient words have been addressed to account for one scan cycle. When the Last Address is reached, block read/write is removed and the address generator returns to Start Address (First Program Word) of the scanner memory. The address generator is signaled to return to Start Address, by a Go to the Scanner Start Address (GTSSA) signal generated by the scanner control circuits. This GTSSA signal is used as the sync command, to bring one trunk scanner into synchronism with the other and to maintain them in synchronism.

This may be best understood with reference to FIG. 6, and the following description. The two trunk scanners are indicated as trunk scanner 25 and trunk scanner 25a, with only that portion of each which is functional to bring and to maintain them in synchronism being shown. The maintenance subsystem (FIG. 1) includes a pair of AND

gates

60 and 61 associated with the

turnk scanners

25 and 25a respectively. A RESET signal can be coupled to both of these AND

gates

60 and 61, when means are activated in the subsystem.

During normal operation, when both

trunk scanners

25 and 25a are operating in synchronism, when the address generator reaches the Last Address, a Last Address signal will occur simultaneously in both trunk scanners 25 and 250. These Last Address signals are coupled to the respective OR

gates

62 and 63, and from the latter to the flip-

flops

64 and 65, setting each of them The flip-

flops

64 and 65 each provide a GTSSA signal to the address generators, to thereby cause them to return to its Start Address. When the Start Address is reached, both the flip-

flops

64 and 65 are reset.

For the purpose of illustrating how the trunk scanners are synchronized when they are not in step, assume that trunk scanner 25a is running behind trunk scanner 25 which is on line. The address generator for the trunk scanner 25 therefore will reach the Last Address first, and will provide the GTSSA signal to the address generator, in the manner described above. Since it is desired to sync the two trunk scanners, the means in the maintenance subsystem will have been activated to couple the RESET signal to the two AND gates and 61. An ON LINE signal likewise is coupled to the AND gate 60, for the trunk scanner 25 is on line.

When the flip-flop 64 sets to provide the GTSSA signal to the address generator, this GTSSA signal also is coupled to the AND gate 60, thus enabling it. The resulting output from the AND gate 60 is coupled to and activates the monostable multivibrator 68, and the latter, in turn, sets the flip-flop via the OR gate 63, to provide a GTSSA signal to the address generator for the trunk scanner 25a. Accordingly, it may be seen that the GTSSA signal provided for the operation of the trunk scanner 25 causes the GTSSA signal for the operation of the trunk scanner 25a to be provided, even though the address generator in the trunk scanner 25a has not reached its Last Address. The address generator in the trunk scanner 25a, therefore, will return to its Start Address, simultaneously with the return of the address generator in the trunk scanner 25 to its Start Address, thereby causing the

trunk scanners

25 and 25a to be in sync.

If the trunk scanner 25a is on line and running ahead of the trunk scanner 25, the operation is the same, in that the GTSSA signal provided in the trunk scanner 25a will cause the GTSSA signal to be generated in the trunk scanner 25, to thereby cause its address generator to advance to its Start Address. In this case, the RESET signal, the GTSSA signal and the ON LINE signal to the AND gate 61 will enable it to, in turn, trigger the monostable multivibrator 67. The latter, via the OR gate 62, will set the flip-flop 64 to provide the GTSSA signal.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained and certain changes may be made in carrying out the above method and in the construction set forth. Accordingly, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Now that the invention has been described, what is claimed as new and desired to be secured by letters Patent is:

I. In a system comprising a memory for storing a plurality of memory words including memory words indicating the status of each of a plurality of trunk circuits, a start address word and a last address word, a pair of trunk scanners operating synchronously and providing redundancy in case of failures, one of said trunk scanners normally being on line" and the other one thereof being on standby, and address generator associated with each of said trunk scanners, said address generators addressing the memory word to be read out of memory and said trunk scanners reading said memory word and performing the functions specified by the contents thereof, said address generators when a predetermined memory word time elapses advancing to address the next memory word in sequential fashion until all of said memory words have been addressed, said trunk scanners each comprising control signal generating means which are set to provide and to couple to said address generators a control signal whensaid address generators address said last address word in said memory to cause said address generators to advance to said start address word and to repeat the addressing of each of said memory words in sequential fashion, said control signal generating means being reset when said address generators address said start address word, and means operable to couple said control signal from said control signal generating means of said trunk scanner which is on line to said control signal generating means of the other one of said trunk scanners, whereby the control signal provided from the trunk scanner which is on line" can be coupled to and used to set the control signal generating means of the other one of said I trunk scanners so that said control signal generating means in both of said trunk scanners are simultaneously set to provide said control signal to cause both of said address generators to simultaneously advance to said start address word, thereby bringing said trunk scanners into synchronism.

2. In the system of claim 1, wherein said means operable to couple said control signal from said control signal generating means of said trunk scanner which is on line" to said control signal generating means of the other one of said trunk scanners comprises a gate associated with each of said trunk scanners, means operable to provide an on line signal to said gate associated with said trunk scanner which is on line, means operable to provide a reset signal to both of said gates, said control signal generating means being coupled to and providing said control signal provided thereby to its associated gate, said gates upon coincidence of said on line, reset and control signals being enabled to set said control signal generating means of the other one of said trunk scanners.

3. The system of claim 2, further including a flip-flop coupled to the output of each of said gates, said gate associated with said trunk scanner which is on line when enabled setting said flip-flop coupled to it to set said control signal generating means of the trunk scanner which is on standby.

4. The system of claim 3, further including an OR gate associated with each of said trunk scanners, the output of said flip-flops being coupled to respective ones of said OR gates, said last address word in said memory being coupled to each of said OR gates, whereby said control signal generating means is set to provide said control signal by either said last address word or by the output of said flip-flop.

5. In a system comprising a memory for storing a plurality of memory words including memory words indicating the status of each of a plurality of trunk circuits, a start address word and a last address word, a pair of trunk scanners operating synchronously and providing redundancy in case of failures, one of said trunk scanners normally being on line and the other one thereof being on standby," an address generator associated with each of said trunk scanners, said address generators addressing the memory word to be read out of memory and said trunk scanners reading said memory word and performing the functions specified by the contents thereof, said address generators when a predetermined memory word time elapses advancing to address the next memory word in sequential fashion until all of said memory words have been addressed, said trunk scanners each comprising control signal generating means which are set to provide and to couple to said address generators a control signal when said address generators address said last address word in said memory to cause said address generators to advance to said start address word and to repeat the addressing of each of said memory words in sequential fashion, said control signal generating means being reset when said address generators address said start address word, a method of synchronizing the operation of said pair of trunk scanners comprising the steps of coupling said control signal from said control signal generating means of said trunk scanner which is on line" to said control signal generating means of the other one of said trunk scanners, whereby the control signal provided from the trunk scanner which is on line can be used to set the control signal generating means of the other one of said trunk scanners so that said control signal generating means in both of said trunk scanners are simultaneously set to provide said control signal to cause both of said address generators to simultaneously advance to said start address word, thereby bringing said trunk scanners into synchronism.

* s a: s

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. Dated OCtObGI" 9,

RICHARD A. PADGETT Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On the Title Page, [73], after "Automatic" add Electric Signed and sealed this 30th day of April l- 9'f1.

(SEAL) Attest:

EDWARD I='I.FLETCEER,JR. C. MARSHALL DAMN Attesting Officer Commissioner of Patents Nov. 13, 1973 DRM P0-105O (10-69) USCOMM-DC 60376-P69 h u.s. GOVERNMENT PRINTING OFFICE :19" o-ass-au.

Claims

1. In a system comprising a memory for storing a plurality of memory words including memory words indicating the status of each of a plurality of trunk circuits, a start address word and a last address word, a pair of trunk scanners operating synchronously and providing redundancy in case of failures, one of said trunk scanners normally being ''''on line'''' and the other one thereof being on ''''standby,'''' an address generator associated with each of said trunk scanners, said address generators addressing the memory word to be read out of memory and said trunk scanners reading said memory word and performing the functions specified by the contents thereof, said address generators when a predetermined memory word time elapses advancing to address the next memory word in sequential fashion until all of said memory words have been addressed, said trunk scanners each comprising control signal generating means which are set to provide and to couple to said address generators a control signal when said address generators address said last address word in said memory to cause said address generators to advance to said start address word and to repeat the addressing of each of said memory words in sequential fashion, said control signal generating means being reset when said address generators address said start address word, and means operable to couple said control signal from said control signal generating means of said trunk scanner which is ''''on line'''' to said control signal generating means of the other one of said trunk scanners, whereby the control signal provided from the trunk scanner which is ''''on line'''' can be coupled to and used to set the control signal generating means of the other one of said trunk scanners so that said control signal generating means in both of said trunk scanners are simultaneously set to provide said control signal to cause both of said address generators to simultaneously advance to said start address word, thereby bringing said trunk scanners into synchronism.

2. In the system of claim 1, wherein said means operable to couple said control signal from said control signal generating means of said trunk scanner which is ''''on line'''' to said control signal generating means of the other one of said trunk scanners comprises a gate associated with each of said trunk scanners, means operable to provide an ''''on line'''' signal to said gate associated with said trunk scanner which is ''''on line,'''' means operable to provide a ''''reset'''' signal to both of said gates, said control signal generating means being coupled to and providing said control signal provided thereby to its associated gate, said gates upon coincidence of said ''''on line,'''' ''''reset'''' and control signals being enabled to set said control signal generating means of the other one of said trunk scanners.

3. The system of claim 2, further including a flip-flop coupled to the output of each of said gates, said gate associated with said trunk scanner which is ''''on line'''' when enabled setting said flip-flop coupled to it to set said control signal generating means of the trunk scanner which is on ''''standby.''''

5. In a system comprising a memory for sToring a plurality of memory words including memory words indicating the status of each of a plurality of trunk circuits, a start address word and a last address word, a pair of trunk scanners operating synchronously and providing redundancy in case of failures, one of said trunk scanners normally being ''''on line'''' and the other one thereof being on ''''standby,'''' an address generator associated with each of said trunk scanners, said address generators addressing the memory word to be read out of memory and said trunk scanners reading said memory word and performing the functions specified by the contents thereof, said address generators when a predetermined memory word time elapses advancing to address the next memory word in sequential fashion until all of said memory words have been addressed, said trunk scanners each comprising control signal generating means which are set to provide and to couple to said address generators a control signal when said address generators address said last address word in said memory to cause said address generators to advance to said start address word and to repeat the addressing of each of said memory words in sequential fashion, said control signal generating means being reset when said address generators address said start address word, a method of synchronizing the operation of said pair of trunk scanners comprising the steps of coupling said control signal from said control signal generating means of said trunk scanner which is ''''on line'''' to said control signal generating means of the other one of said trunk scanners, whereby the control signal provided from the trunk scanner which is ''''on line'''' can be used to set the control signal generating means of the other one of said trunk scanners so that said control signal generating means in both of said trunk scanners are simultaneously set to provide said control signal to cause both of said address generators to simultaneously advance to said start address word, thereby bringing said trunk scanners into synchronism.